1. Field of the Invention
This invention relates generally to the field of semiconductor device manufacturing and, more particularly, to a method and apparatus for hierarchical process control.
2. Description of the Related Art
To fabricate a semiconductor device, a wafer is typically processed through numerous processing tools in a predetermined sequence. The processing tools may include photolithography steppers, etch tools, deposition tools, polishing tools, rapid thermal anneal tools, ion implantation tools, and the like. Each processing tool modifies the wafer according to a particular operating recipe. For example, a photolithography stepper may be used to form a patterned layer of photoresist above the wafer. Features in the patterned layer of photoresist correspond to a plurality of features, e.g. gate electrode structures, which will ultimately be formed above the surface of the wafer. The tool sequence, as well as the recipes used by the tools, must be carefully controlled so that the features formed on the wafer meet appropriate design and performance criteria. Thus, advanced process control (APC) systems are often used to coordinate operation of the processing tools.
Individual tools may be controlled using feedback and/or feed forward techniques. For example, tool sensors may be used to sense conditions or process parameters in the tool. A controller may then determine one or more inputs so that the conditions and/or process parameters of the tool remain within a selected tolerance of one or more target values associated with the conditions and/or process parameters. The determined inputs are then fed back or fed forward to the appropriate tool, which may use the determined inputs to process one or more wafers. For another example, a metrology tool may be used to measure one or more parameters of a wafer processed in a tool. The measured parameters may be compared to target values of the measured parameters and the comparison may be used to adjust an operating recipe of the tool.
Controlling tools using conventional feedback and/or feed forward techniques may become cumbersome as the number of tools in a production line and/or fabrication facility increase. Moreover, conventional feedback and/or feed forward techniques may not adequately account for errors or deviations from desired targets caused by the interaction of processes performed by different tools. These types of errors and/or deviations from desired target values may increase significantly as the number of tools in the production line and/or fabrication facility increases.
The present invention is directed to addressing the effects of one or more of the problems set forth above.